1. Field of the Invention
Exemplary embodiments relate to a method for driving a display panel, and a display apparatus for performing the method for driving the display panel. More particularly, exemplary embodiments relate to a method for driving a display panel having cholesteric liquid crystal, and a display apparatus for performing the method for driving the display panel including cholesteric liquid crystal.
2. Description of the Related Art
Generally, a typical liquid crystal has regularly arranged molecules and fluidity similar to that of a liquid. In addition liquid crystal molecules have various optical characteristics according to an arrangement direction thereof.
The typical liquid crystal has long and narrow molecules, e.g., molecules shaped like a rod. The arrangement of the molecules is changed or the motion of the molecules may be scattered by an electric field, a magnetic field, heat, etc. from an outside controller. Therefore, the optical characteristics of the liquid crystal may be easily changed.
The liquid crystal may be classified into different types of liquid crystal such as nematic liquid crystal or cholesteric liquid crystal according to the arrangement of the molecules therein. The arrangement, e.g., positioning, of the molecules in the nematic liquid crystal is irregular but the molecular axis of the nematic liquid crystals is commonly oriented in a particular direction. The direction of the axis alignment of molecules arranged in an upper portion of the liquid crystal is substantially the same as that in a lower portion of the liquid crystal so that polarization is offset in both directions. Thus, the nematic liquid crystal does not have ferroelectricity. The cholesteric liquid crystal has a layer structure having a plurality of layers, and the arrangement of the molecules in each of the layers is similar to the arrangement of nematic liquid crystal, e.g., the positional relationships of liquid crystal molecules within a single layer is irregular, but the axis alignment of the molecules is common to the layer. Each of the layers is typically very thin. The arrangement of the molecules in each layer is directed in a longitudinal axis, and surfaces of the layers are parallel with, e.g., normal to, each other. The longitudinal axis of each of the layers is a little different from the longitudinal axis of adjacent layer, so that the arrangement of the molecules in the cholesteric liquid crystal is typical of a spiral nature.
FIGS. 1A, 1B and 1C are schematic diagrams illustrating a state change of cholesteric liquid crystal according to the intensity of an electric field applied thereto.
Referring to FIG. 1A, when an electric field E applied to the cholesteric liquid crystal is greater than a first electric field EC, the cholesteric liquid crystal is arranged to be in a homeotropic state. Referring to FIG. 1B, when the electric field E becomes less than a second electric field EF in the homeotropic state, the cholesteric liquid crystal is arranged to be a planar state. Referring to FIG. 1C, when the electric field E is greater than the first electric field EC and less than the second electric field EF in the homeotropic state, the cholesteric liquid crystal is arranged to be a focal conic state. The cholesteric liquid crystal in the planar state reflects light having a specific wavelength, and the cholesteric liquid crystal in the focal conic state scatters the light.
The cholesteric type of liquid crystal is gaining in popularity as a new medium for a reflective display apparatus, but has a relatively slower transition period with respect to the electrical field applied thereto. Thus, the typical cholesteric liquid crystal is not suitable for displaying rapidly changing display states, e.g., a video.